The special U.S. and Canadian envoys on acid rain have completed their joint report to their two governments. Its great contribution is its realism. In a letter to the president yesterday, U.S. envoy Drew Lewis said "these recommendations will not please everyone. Some people will contend we have recommended nothing to reduce the flow of transboundary air pollutants. Others will contend we have recommended an outlay of funds disproportionate to the value of an environmental improvement."

He asked that the report be judged not as a solution to the problem but a start, "the most sensible steps we can take, given the different viewpoints of our two countries," the sharp differences over the issue in this country and "our uncertain scientific understanding of the probl fair standard, we think, and one according to which Mr. Lewis and his Canadian counterpart, William Davis, did well.

Under the terms that they propose:

*The United States for the first time would officially acknowledge the existence of the problem and that power plant and other industrial emissions are its basic cause. No more being cute about it, no more mock agnosticism. The U.S. side of the report does still tiptoe as to the extent of the damage done. But it does not pretend there is none.

*Canada would, if not agree, at least accept that there is no instant solution to the problem. The report recommends no specific reductions in emissions or even specific means to achieve reductions. And it recognizes that "the available control options" all have a "high cost."

*To find ways to reduce these costs, the United States would spend $5 billion over the next five years on "commercial demonstration" of new technologies. Half this money would come from the federal governmnt, half from industry, the envoys propose. Presumably the industry half would be passed on in higher rates and prices.

In past years the administration has stoutly resisted spending large sums on acid rain, on grounds that more research was needed. This would take it past that point, and in the least convenient of budget years. The president, who has a meeting scheduled with Canadian Prime Minister Brian Mulroney here in March, should do it anyway. There is no blinking the problem, in either environmental or diplomatic terms. Canadians believe, with cause, that the United States is using their country as a dumping ground. Damage occurs in this country as well. There is in the report an implicit commitment that the U.S. government will someday move to cut emissions. How much is deliberately left for later. Each side gives and gets a little, and the process starts. That is better than a lot of the alternatives.